(1) Field of the Invention
The present invention relates to a multihead serial printer which can be used as a printing apparatus for a terminal portion of a computer or a word processor.
(2) Description of the Prior Art
Japanese Patent Application Laid-Open Specification No. 163670/83 discloses three methods. According to the first method, wires of a single head are divided into three groups in the carriage spacing or line direction and the respective groups can be independently moved in the paper feeding or row direction. According to the second method, three printing heads are arranged on one carriage serially in the row direction. According to the third method, printing heads are mounted on three carriages and arranged serially in the row direction.
In each of the above-mentioned methods, the high-speed printing mode and the high-density printing mode can be changed over to each other, and these methods are characterized in that by one printer, alphabetic letters, numeral figures and kana letters can be printed at a high speed and Chinese characters (kanji) can be printed. Among the above-mentioned three methods, the third method is especially versatile and optimum printing operations can be performed for various printing formats.
However, the third method is defective in that since carriages are arranged with one another serially in the row direction, the size of the apparatus is increased. Furthermore, three pairs of guide shafts (6 shafts) are necessary, and since overlap printing by change of lines is carried out in the low-speed and high-density printing mode, the paper feeding quantity should be controlled very precisely. Accordingly, this method is defective in that the printing grade is low.
Japanese Patent Application Laid-Open Specification No. 161184/81 and U.S. Pat. No. 4,332,249 disclose techniques of attaching a motor to a carriage and moving the carriage along a guide shaft. According to these techniques, a pinion gear is rotated by the motor and is engaged with a rack gear mounted on the guide shaft to move the carriage. Precise moving of the carriage is attained. However, since only one carriage is arranged, high-speed printing cannot be performed, and high-density printing is difficult.